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1 | =pod |
2 | ||
3 | =head1 NAME | |
4 | ||
5 | SSL_CTX_set_async_callback, | |
6 | SSL_CTX_set_async_callback_arg, | |
7 | SSL_set_async_callback, | |
8 | SSL_set_async_callback_arg, | |
9 | SSL_get_async_status, | |
10 | SSL_async_callback_fn | |
11 | - manage asynchronous operations | |
12 | ||
13 | =head1 SYNOPSIS | |
14 | ||
15 | =for comment multiple includes | |
16 | ||
17 | #include <openssl/ssl.h> | |
18 | ||
19 | typedef int (*SSL_async_callback_fn)(SSL *s, void *arg); | |
20 | int SSL_CTX_set_async_callback(SSL_CTX *ctx, SSL_async_callback_fn callback); | |
21 | int SSL_CTX_set_async_callback_arg(SSL_CTX *ctx, void *arg); | |
22 | int SSL_set_async_callback(SSL *s, SSL_async_callback_fn callback); | |
23 | int SSL_set_async_callback_arg(SSL *s, void *arg); | |
24 | int SSL_get_async_status(SSL *s, int *status); | |
25 | ||
26 | =head1 DESCRIPTION | |
27 | ||
28 | SSL_CTX_set_async_callback() sets an asynchronous callback function. All SSL | |
29 | objects generated based on this SSL_CTX will get this callback. If an engine | |
30 | supports the callback mechanism, it will be automatically called if | |
31 | SSL_MODE_ASYNC has been set and an asynchronous capable engine completes a | |
32 | cryptography operation to notify the application to resume the paused work flow. | |
33 | ||
34 | SSL_CTX_set_async_callback_arg() sets the callback argument. | |
35 | ||
36 | SSL_set_async_callback() allows an application to set a callback in an | |
37 | asynchronous SSL object, so that when an engine completes a cryptography | |
38 | operation, the callback will be called to notify the application to resume the | |
39 | paused work flow. | |
40 | ||
41 | SSL_set_async_callback_arg() sets an argument for the SSL object when the above | |
42 | callback is called. | |
43 | ||
44 | SSL_get_async_status() returns the engine status. This function facilitates the | |
45 | communication from the engine to the application. During an SSL session, | |
46 | cryptographic operations are dispatched to an engine. The engine status is very | |
47 | useful for an application to know if the operation has been successfully | |
48 | dispatched. If the engine does not support this additional callback method, | |
49 | "ASYNC_STATUS_UNSUPPORTED" will be returned. See ASYNC_WAIT_CTX_set_status() for | |
50 | a description of all of the status values. | |
51 | ||
52 | An example of the above functions would be the following. | |
53 | 1. Application sets the async callback and callback data on an SSL connection | |
54 | by calling SSL_set_async_callback(). | |
55 | 2. Application sets SSL_MODE_ASYNC and makes an asynchronous SSL call | |
56 | 3. OpenSSL submits the asynchronous request to the engine. If a retry occurs at | |
57 | this point then the status within the ASYNC_WAIT_CTX would be set and the async | |
58 | callback function would be called (goto Step 7). | |
59 | 4. The OpenSSL engine pauses the current job and returns, so that the | |
60 | application can continue processing other connections. | |
61 | 5. At a future point in time (probably via a polling mechanism or via an | |
62 | interrupt) the engine will become aware that the asynchronous request has | |
63 | finished processing. | |
64 | 6. The engine will call the application's callback passing the callback data as | |
65 | a parameter. | |
66 | 7. The callback function should then run. Note: it is a requirement that the | |
67 | callback function is small and non-blocking as it will be run in the context of | |
68 | a polling mechanism or an interrupt. | |
69 | 8. It is the application's responsibility via the callback function to schedule | |
70 | recalling the OpenSSL asynchronous function and to continue processing. | |
71 | 9. The callback function has the option to check the status returned via | |
72 | SSL_get_async_status() to determine whether a retry happened instead of the | |
73 | request being submitted, allowing different processing if required. | |
74 | ||
75 | =head1 RETURN VALUES | |
76 | ||
77 | SSL_CTX_set_async_callback(), SSL_set_async_callback(), | |
78 | SSL_CTX_set_async_callback_arg(), SSL_CTX_set_async_callback_arg() and | |
79 | SSL_get_async_status() return 1 on success or 0 on error. | |
80 | ||
81 | =head1 HISTORY | |
82 | ||
83 | SSL_CTX_set_async_callback(), SSL_CTX_set_async_callback_arg(), | |
84 | SSL_set_async_callback(), SSL_set_async_callback_arg() and | |
85 | SSL_get_async_status() were first added to OpenSSL 3.0.0. | |
86 | ||
87 | =head1 COPYRIGHT | |
88 | ||
89 | Copyright 2019 The OpenSSL Project Authors. All Rights Reserved. | |
90 | ||
91 | Licensed under the OpenSSL license (the "License"). You may not use | |
92 | this file except in compliance with the License. You can obtain a copy | |
93 | in the file LICENSE in the source distribution or at | |
94 | L<https://www.openssl.org/source/license.html>. | |
95 | ||
96 | =cut |